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SCN Sampling (08/31/17)

When to sample, where to sample, how to sample and more answered.

SCN Sampling

When to sample? Sample in the fall when SCN egg levels are highest, and consequently, the most likely time of year to detect SCN. Sampling can be done before or after harvest, but it should be done before any tillage is done in the field.

Where to sample? SCN moves with soil, so consider the most likely way SCN-infested soil might be brought into a field. Additionally, consider “suspicious” areas. The most important areas (Figure 1) to consider include:

markell.scn.sampling

  • Field entrance: SCN-infested soil often moves into new fields on equipment. Movement on equipment is the most common way the pathogen transfers and is thought to be responsible for its expansion across the U.S.
  • Flood-prone areas and low spots: Cysts will move with water, so areas that are prone to flooding and water pooling are likely areas where SCN will be introduced. SCN can be moved by birds, on their bodies and in their digestive tracts, and birds frequently visit wet spots in fields.
  • Shelter belts: Cysts can move in dust storms or high winds and are deposited as the wind speed slows. In North Dakota, this usually means shelter belts.
  • Yellow spots showing up in August: The damage from high SCN levels usually begins to appear in August, especially if plants are water-stressed. Any lens-shaped areas of fields turning yellow in August are suspicious.
  • High pH: High pH soils are very favorable to SCN and, as a result, SCN damage often is noticed first in high pH spots in fields.

            How to sample?

  • Go where SCN is, and aim for the roots. Sampling is most effective when the samples are collected within a few inches of the soybean stem and 6 to 8 inches deep into the soil.
  • More samples are better. Take 10 to 20 soil cores or thin shovel slices in a suspicious area and bulk the sample.
  • Keep the sample relatively cool and get it to the lab quickly. SCN is a tough worm, but SCN will struggle if the sample sits on the dash of a pickup in the August sun.

            What do the results mean?        Lab results will be presented as eggs/100 cc soil, which is the number of eggs in approximately a 6-ounce can. “J2,” which refers to the second-stage juvenile worm, also may be included. Think of the egg level as your “risk” factor: the higher the number, the greater the risk. Very low levels (less than 100) could be false positives and should be viewed with some caution. We recommend resampling. Very high levels (greater than 10,000 egg/100 cc) likely will impact soybean production for years to come.

            What do you do if you have SCN?          We recommend beginning management strategies if you find any positive samples.

            What do you do if you don’t find SCN?  Be vigilant and sample again next year.

Sam Markell

Extension Plant Pathologist, Broad-leaf Crops

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